Immunogenicity and protective efficacy of an inactivated SFTS vaccine candidate in mice

Severe fever with thrombocytopenia syndrome (SFTS), caused by a novel identified bunyavirus SFTS virus (SFTSV), was an emerging viral infectious disease that was firstly reported in China. There are no licensed vaccines and therapeutics against SFTSV currently. B-Propiolactone (BPL) inactivated whole virions of SFTSV strain AH12 were prepared as experimental vaccine in different antigen dose with or without Al(OH)3 adjuvant. The experimental SFTS vaccine was a satisfying immunogen, which could efficiently trigger the development of high levels of SFTSV NP-specific IgG antibodies and neutralizing antibodies against SFTSV Strain HB29 in BALB/c and C57/BL6 mice, and could induce SFTS virus-specific cellular immune responses to a certain extent. A single dose of vaccine was immunogenically insufficient in BALB/c mice; the second and third dose resulted in significant boost in antibody response. The use of Al(OH)3 adjuvant resulted in higher antibody titers. The mediate-dose of vaccine could induce as high and equivalent level of antibody titer as that of high-dose. The experimental SFTS vaccine in mediate- and high antigen dose with adjuvant resulted in solid protection of C57/BL6 mice against wild-type SFTSV challenge with markedly accelerated virus clearance from blood and spleen compared with controls. The experimental SFTS vaccine prepared in this study could efficiently elicit virus specific humoral and cellular immune responses in both BALB/c and C57/BL6 mice, and could protect C57/BL6 mice against SFTS virus challenge. These results supplied evidence that inactivated vaccine was a promising vaccine candidate for the prevention of SFTSV infection.